There are many environments where separation of liquid/particles mixtures is desirable. A difficulty that has often been encountered in the separation process concerns the loss of many of the finer particles. This occurs during the separation process where the fine particles are often too small to be captured by the separation medium and pass with the separated medium. Reclamation of these particles is extremely difficult and often too impractical and costly.
An example of a pertinent environment is in connection with the processing of coal. Coal from the mines is ground and classified into several fractions. A common system would be to send a 11/2 inch.times.0 fraction into the plant and make an initial separation into two fractions 11/2.times.1/4 inch and 1/4.times.0. The 1/4.times.0 is then separated into 1/4 by 28 mesh and 28.times.0. The 28.times.0 particles are called coal fines. As part of the cleaning and sizing of coal, a preparation plant must contend with these coal fines, that is coal particles finer than a 28 mesh screen.
In the past, these coal fines were separated by dissolved air floatation cells and dewatered on disc filters. The disc filters will dewater the fines to approximately 24% moisture. In a relatively large preparation plant, up to 150 tons per hour of fines are produced.
There is a desired in the industry to reduce the moisture content of the fine fraction. Drying is one alternative, however, it is expensive and a long term pollution source. An alternative is mechanical dewatering. It appears that a dryness of 15% moisture is the general target, with some preparation plants striving for 121/2% because of customer demands.
Dewatering of material has been accomplished in various industries in a variety of different ways, for example, mechanical devices such as vacuum augmented dewatering tables have been used in the papermaking industry for dewatering pulp and similar types of slurries.
A recent concept that has been gaining acceptance involves the principle of double-sided dewatering at the couch. This involves a couch press as a felted lump breaker roll. In principal, it is an inverted press with a special felt that works according to the transversal flow principle. The felt is designed so that it can receive considerable amounts of water. This water is then removed from the felt with effective suction pipes before its re-entry into the press nip. The increased dewatering, obtained partially through pressure and partially through double-sided dewatering, gives sizable gains in dry content. Increased water removal is obtained from both the double-sided dewatering at the couch and through the added pressure of the couch nip.
Other developed principles are also of interest. For example, in U.S. Pat. No. 3,138,088, the concept of using a mat of coarse particles as a base upon which finer particles can be collected is contemplated.
It would certainly be advantageous if principles of the above type could be adapted for use in a system for facilitating the dewatering of material such as coal fines and to enhance the amount of reclaimed coal fines in such a process.